Rapamycin derivative (RAD) is a macrolide metabolite with potent and unique immunosuppressive properties. RADB 253 is a two-year multicenter investigation of the safety, pharmacokinetics and efficacy of RAD in De Novo heart transplant recipients. Subjects will receive one of two RAD doses 1.5 mg/day or 3.0 mg/day) and azathioprine placebo or RAD placebo and 1.0-3.0 mg/kg/day of azathioprine and will be randomized 1:1:1. Treatment will be double-blind and will continue for 24 months post-transplant. Subjects will receive RAD study drug and azathioprine placebo or azathioprine drug and RAD placebo in combination with cyclosporine and steroids and will not receive anti-lymphocyte induction. Patients will be screened prior to transplant and randomized immediately post-transplant. RADB will be formulated as oral tablets and administered twice daily with Neoral cyclosporine. Patients will undergo frequent safety laboratory assessments and three 8-hour pharmacokinetic sessions at 2, 3 and 6 months post-transplant.